Anim. Behav., 1979, 27, 669-685

FISH CLEANING SYMBIOSIS : PROXIMATE CAUSES OF HOST BEHAVIOUR

BY GEORGE S. LOSEY, JR Department of Zoology and Hawaii Institute of Marine Biology, University of Hawaii, Honolulu, Hawaii

Abstract. Proximate causes for response to a cleaner fish were studied in two host fishes, Chaetodon auriga and Zebrasoma fiavescens. Response to a model of a cleaner fish indicated whether ectoparasites, deprivation of exposure to the model, and aversive stimulation had any effect on cleaning symbiotic behaviour. Tactile reinforcement and conflict behaviour appeared to be the major causal factors for host behaviour . Deprivation of experience with the model and aversive stimulation had strong effects on these factors . Ectoparasites had little effect on C. auriga and only amplified responses in Z. flavescens. An evolutionary scheme is suggested in which some cleaner fish have exploited their hosts' tendency to respond to rewarding tactile stimuli .

Cleaning symbiosis is an interspecific relation- from other sources such as fish eggs and zoo- ship found in many types of environments and plankton. They could exist as mutualist, com- is most widespread among fishes. Cleaning is mensal, or parasite depending on their diet very common among coral reef fishes but is also (Losey 1972a, 1974) . Some cleaners, particularly found in many freshwater species . Recent reviews Labroides species, show parasitic feeding . They are in Potts (1973) and Losey (1978) . chase uncooperative hosts and often bite them Cleaning is thought to be a mutualism . In a repeatedly (personal observation) . Or, they typical interaction for tropical reef fishes, the cause the host fish to stop and pose by beginning host fish approaches a cleaner fish in the cleaner's to inspect it while it is avoiding the cleaner territory or cleaning station . The host fish poses (Potts 1973) . or solicits the attention of the cleaner by assu- Ectoparasite removal probably can be adaptive ming an unusual posture such as tail stand and for hosts (Limbaugh 1961 ; Youngbluth 1968 erecting its fins . Either before or after the host Hobson 1971 ; Losey 1972a, 1974 ; Atkins & poses, the cleaner engages in inspecting beha- Gorlick MS.), but there is only anecdotal viour, a composite of action patterns including evidence for any proximate causal influence by swimming close, orienting to the host, and ectoparasites (e .g. Feder 1966). Host fish in contacting the host with its mouth, pelvic fins, different areas show similar behaviour regardless and/or caudal fin . The cleaner may feed on the of the mutualistic to parasitic form of the body surfaces or inside the mouth and gills of symbiosis (Losey 1974). Study of immediate the host . Hosts frequently jerk or twitch during causation is needed to assess the effects of the cleaning process as a signal of their intention ectoparasites and explain the remarkably similar to depart (Feder 1966) . behaviour shown by host fish throughout the Symbiosis can be classified by population world. growth rate (Odum 1959) and metabolic de- Fricke (1966) showed that host fish will pose pendency (Cheng 1967) of the symbionts . These for a model of a cleaner fish . I made unsuccessful dimensions of classification detract from potenti- attempts to use this response to assess the ally misleading interpretations of `harm versus influence of ectoparasites on host behaviour benefit to the symbionts' . Lincicome (1971) (Losey 1971, unpublished results) . One reason argued that the effects of interacting with another for the failure of these attempts was the rein- species lie along many dimensions that jointly forcing nature of experience with the cleaner determine the value of the relationship. 'Para- model (Losey & Margules 1974) : fish's reactions sites' that appear harmful may, under some to the model changed after experience with the conditions, be of positive survival value to the model. Unpublished research by Lynn Margules host. attempted to correlate ectoparasitic infections Conversely, mutualists might be parasitic under with learning performance . She measured various some conditions . Cleaners feed on varying parameters of instrumental conditioning per- proportions of mucus (Gorlick 1978), ectopara- formance, using presentation of a cleaner model sites, and host tissues as well as occasional food as a reinforcement . Her results were negative

669

670 ANIMAL BEHAVIOUR, 27, 3

except for an indication of a relationship between flavescens, a tropical marine surgeon fish . ectoparasites and resistance to extinction of the Notes at the end of this section describe features instrumental response . that differed from the final study on C. auriga. This paper is the second of two studies aimed Adult fish were captured on reefs in Kaneohe at more direct appraisal of the causation of Bay, Hawaii, that were inhabited by the Hawai- host behaviour. In the present study, fish were ian cleaner wrasse Labroides phthirophagus . given continuous access to a cleaner model . I Fish were held in pens at the Hawaii Institute estimated the magnitude of various behavioural of Marine Biology for up to two weeks prior to patterns that are important to cleaning symbiosis . use. Fish that did not show abraded body surfaces or obvious indications of disease were Methods selected. For the duration of the study, they were Methods were designed to train an individual to assigned to a treatment group as parasitized or enter a transparent response box in order to unparasitized, and deprived or not deprived . interact with a cleaner model. The major goal One fish was placed in the test compartment at was to give ectoparasitic infection a chance to each end of a 1400-litre aquarium (Fig. 1) show a causal effect on host behaviour . I separated by a central chamber with an opaque analysed for differences in the behaviour of divider. Test compartments contained a brick parasitized and unparasitized fish under different and coral shelter with otherwise bare sub- conditions of deprivation of exposure to the stratum . model, aversive stimulation, and length of The experimental sequence (Table I) began exposure to the model . I also hoped to reveal with two days of treatment with 0 . 4 to 0 . 6 the general form of the causal system for host ppm copper sulphate to remove ectoparasites . responses by observing the effects of all of these On the evening of day 2, copper was flushed variables on cleaning symbiotic responses . from the tanks and, if the fish had been assigned to the parasitized group, 5 to 20 parasitic Experimental Design cymothoid isopods were added to the tank . Two experimental designs were used for the These parasites grasp their host firmly with host species Chaetodon auriga, a tropical marine sharp legs. They feed deep in the flesh of the butterflyfish. The `final study' incorporated animals and leave large eroded areas that are various improvements over an `early study' . An usually inflamed with bacterial infections . abbreviated version of the final study was con- On day 3, a realistic model of L. phthirophagus ducted with a second host species, Zebrasoma on the end of a 0 . 4-cm diameter stainless steel

Solenoid

Photocell

Mirror chips Black Cover J Light Lr

Dither Test

Fig. 1 . A schematized drawing of the experimental aquarium . Two test chambers are shown. The C. auriga shown entering the response box on the left would be classed as in-box but is not occluding the light beam or touching the cleaner model . See Methods section for explanation. LOSEY : CAUSES OF CLEANING 671

Table I. Experimental Calendar for the Four Treatment Groups

Treatment Group Not deprived Deprived Day Parasitized Unparasitized Parasitized Unparasitized I Copper treat . Copper treat . Copper treat . Copper treat. 2 Copper treat . Copper treat . Copper treat . Copper treat . 3 Infect and train Train Infect and train Train 4 Train Train Train Train 5 Control day Control day Control day Control day 6 Test day Test day Deprive Deprive 7 Suppression Suppression Deprive Deprive 8 Test day Test Day 9 Deprive Deprive 10 Deprive Deprive 11 Suppression wire was introduced into the aquarium by a subsequent `test day' the model was introduced rotary solenoid . It was moved over an arc of into the response box for 6 h . Time in the I to 2 cm at about one cycle per second near the response box was recorded . Videotape record- bottom of the tank . After the fish approached ings of each fish's activities were made from an and was contacted by the model, it was placed adjacent room with one 9-min sample during on a shorter wire near the surface of the water. each hour of the test day . The model was then enclosed in a 12 x 9 >: 30 The fish were then deprived according to the cm response box of clear Plexiglass with only same group assignment and then exposed to a one entrance (Fig . 1). Fish were trained to `suppression day' during which the model was enter this box in order to contact the model . presented for 7 h . During hours 2, 4, and 6, an This behaviour is an unlikely event in the 80-W spotlight just over the response box and absence of an attractive stimulus in the box . under the opaque black cover (not shown in Fish were trained on days 3 and 4 and dis- Fig. 1) was illuminated for 1 h as an aversive carded if they did not meet the criterion of stimulus . Behavioural recordings were made as spending a cumulative time of 30 min in the on the test day . At the end of the day all fish response box by the end of day 4 . After the fish were killed and assayed for ectoparasites and met the criterion, the model was removed from condition of body surfaces . the water. On day 5 (control day) the fish were exposed Two types of `control' fish were run for C . to 6 h of continuous access to the model as an auriga only . `Bare-wire' fish were trained as ad libitum ration of the stimulus . The amount above but the model was removed from the wire of time spent in the response box next to the prior to introducing the response box . Fish model was sensed by a photocell and recorded . were trained to the model, then to the wire The photocell was trained on a focussed light alone, and finally to enter the response box beam that was reflected over a complex path enclosing the wire. Only the bare wire was used through the box by four mirror chips (Fig . 1). on the control and test days . They were not Fish could not contact the model without subjected to a suppression day . `No-wire' fish occluding the light beam in some portion of its were trained normally but were given no wire or path. I could not record actual contact between model on control, test, and suppression days . the model and the fish, but the dimensions of In the early study on C. auriga, fish were not the response box assured that the fish were treated with copper sulphate and were infected nearly always in contact with the model when only by ectoparasites acquired prior to capture they occluded the light beam . or while in the holding pens . Z. lavescens were Following day 5, the fish were deprived of not treated with copper due to adverse effects exposure to the model either overnight (not of such exposure found in this species . However, deprived) or for two days (deprived), according ectoparasites were rarely found and induced to their previous group assignment. On the isopod infections were successful . The early

672 ANIMAL BEHAVIOUR, 27, 3

study on . auriga used the first of two in- Table II. Number of Individuals in Each Treatment Group dividuals to respond to the model and thus may have selected for more response-prone individu- Not als. Z. flavescens were not exposed to a sup- Species and parasite group deprived Deprived pression day. Chaetodon auriga-early study clean 1 Behaviour Patterns -c 10 parasites 2 The following behavioural units were re- 10 to 50 parasites 10 corded : (i) response duration, i .e. time spent in > 50 parasites 6 the response box as sensed by the photocell and Chaetodon auriga-final study recorded continuously on an event recorder ; clean 5 5 (ii) in-box duration, i .e. time spent with any parasitized 5 5 portion of the body in the response box ; (iii) Chaetodon auriga-bare-wire controls tilt duration, i .e. time spent in a head-down clean 1 (greater than 15 °) position while in the response parasitized 4 box divided by time in-box ; (iv) fin-erect duration, i .e. time spent with the dorsal, anal, Chaetodon auriga-no-wire controls clean 1 or pelvic fins erected while in the response box parasitized 1 divided by time in-box ; (v) wag, i .e. the number of exaggerated lateral movements of the head Zebrasoma lavescens without forward propulsion; (vi) twitch, i .e . clean 8 the number of fast movements of any body parts parasitized 5 that were not associated with propulsion ; (vii) jump, i .e. the number of extremely fast forward movements of the body usually less In the final study on C. auriga, parasitized than one body length forward ; (viii) chafe, i .e. individuals carried from one to three cymothoid the number of rubs against the substratum . isopods. A few 'unparasitized' or `clean' Measures (ii) to (viii) were taken from video- individuals were infected on their gill filaments tape recordings . by small numbers of tiny crustaceans that Tilt and fin-erect are common elements of appeared to be larval lernaeid copepods . These posing or cleaning solicitation behaviour . Wag, parasites were only lightly attached and, com- twitch, and jump are movements that appear pared to the cymothoid isopods, should have to serve as warning signals to the cleaner. caused little if any stimulation of their hosts . Parasitized Z. flavescens were infected by one Sample Sizes and Parasite Loads to seven cymothoid isopods, occasional mono- Of the 87 C. auriga originally selected, 38 geneid trematodes and, on one individual, a animals were rejected due to disease, infestation single lernaeid copepod on the body surface . by unwanted parasites, failure to meet the response criterion, or equipment failure . Re- Data Analysis maining sample sizes for all groups are presented Observations of the behavioural patterns in Table II . were analysed in a series of steps. The negative In the early study on C. auriga, the fish were results of earlier studies prompted me to give divided into four groups based on the number ectoparasitic infections every possible chance to of ectoparasites found : clean or no parasites ; show some relationship to host behaviour . Steps light or fewer than 10 parasites ; moderate or early in the analysis divided each individual's from 10 to 50 parasites ; and heavy or greater response record into a sequential series of tabula- than 50 parasites . Parasites in the early study tions for each day in order to reveal changes included monogeneid trematodes, cymothoid within a single day. Later steps utilized a single isopods, and caligoid and lernaeid copepods . data point to describe each behavioural pattern The heavily parasitized fish had much abraded for each individual on each day to reveal trends tissue and would probably have died if held in that were characteristic of the entire day. Some captivity for a few more weeks without treat- steps were omitted when a particular block of ment. The parasite groups had disparate sample data was insufficient to support the statistical sizes in this study since ectoparasites could only technique. be assayed after the experiments by killing the Twelve-min measures. The first step was to fish, and because clean individuals were rare . reveal any trend in the response duration rates LOSEY : CAUSES OF CLEANING 673 for each individual during the control and test changes in the other behavioural patterns regard- days. The event records for response duration, less of treatment . as sensed by photocells on each 6-h day, were Secondary attention was given to the results divided into 30 12-min segments for each of the analysis of variance for treatment group, individual . A correlation coefficient (r) was particularly when ectoparasite or deprivation calculated for each individual as the relation- treatments were shown to interact with an hour ship between the duration of response and the of testing . The latter tests were examined since average response bout length per segment and the effects of several treatments were not seen the sequential number of the segment . Only until the last 2 to 3 h of the day . Overlap between response duration could be treated in this treatment groups early in the day reduced the manner since continuous records were not differences between groups in the averages for available for the other behavioural patterns . the entire day (below) . However, these results Hourly estimates. The second step was to must be treated with caution since estimates for reveal hourly trends in all behavioural patterns one hour were not independent of those for while allowing for any effects of experimental other hours . The apparent sample size was treatments. For both control and test days, a inflated. For example, 20 individuals were used set of six hourly estimates of response duration in the final study on C. auriga, but I have one was obtained for each individual by finding the hourly estimate for each individual during each median 12-min measure for each hour. Hourly hour. As a result, 120 data points were included estimates for all other behavioural patterns in the analysis of variance for the test day, were taken from the 9-min videotape records that had six categories for the hour-of-testing that were taken on every hour of the test and variable . suppression days . Estimates were tabulated for Daily estimates . The third step was to provide each individual as the percentage of duration a single estimate of the amount of behaviour for of the 9-min sample period for the time estimates each individual on each day (in-box, tilt, and fin-erect) and the mean number . This estimate per minute during the 9-min sample for counts allowed testing for the effects of ectoparasites, (wag, twitch, jump, and chafe) . deprivation, and aversive stimulation without Three analyses were performed on these data the inflated sample size of the hourly estimates . (i) an analysis of covariance used hour of The mean hourly estimate for each individual testing as a covariate and test individual as a was taken as its daily estimate . variable category for both control and test days . Three types of analysis were performed : This test indicated any linear relationship be- (i) a rank sum test for differences between tween behaviour and hour of testing for the entire ectoparasite groups having the same deprivation group. (ii) A parametric, three-way analysis treatment ; (ii) a parametric, two-way analysis of variance was performed where variable of variance with variable categories of ecto- categories were hour of testing, ectoparasite parasite and deprivation group for the control group, and deprivation group . This analysis was and test days ; (iii) for the suppression day, primarily intended to indicate any relationship separate daily estimates for three periods of the between behaviour and hour of testing while day : hour 1 ; hours when the aversive stimulus removing any effects of the other variables . was present ; and hours 3, 5, and 7 after the aver- (iii) Correlation coefficients (r) were calculated sive stimulus had been removed. These data were for the relationship between response duration analysed by parametric, three-way analysis of and the duration or rates of other behavioural variance with variable categories of aversive patterns . Coefficients were calculated for homo- versus non-aversive hours, ectoparasite, and geneous groups, that is, those treatment groups deprivation treatment to appraise the effects of indicated as not statistically different by the aversive stimulation . They were also analysed analysis of variance above . These tests were by parametric, two-way analysis of variance with performed to indicate whether apparent cor- variable categories of ectoparasite group and relations between action patterns and depriva- deprivation group, with a separate analysis for tion or ectoparasite treatment might be an non-aversive and aversive hours . The latter indirect result of a correlation to response tests were to appraise the effects of treatments duration. I suspected that the treatment might under the influence of aversive stimulation. cause differences in the amount of time in-box Daily differences . High variability between while the amount of time in-box might lead to individuals threatened to conceal effects caused

674 ANIMAL BEHAVIOUR, 27, 3

by deprivation and aversive stimulation . Daily Response of both parasitized and clean groups differences were used to indicate day-to-day decreased throughout each day of testing changes in an individual's daily estimates . (P < 0.01 by analysis of covariance of hourly Differences were calculated by subtracting the estimates, n = 78). Correlation coefficients for daily estimates for each individual as follows : the 12-min measures of response duration were test day minus control day, hour 1 of suppression negative for 9 of the 13 individuals on the control day minus test day, aversive hours of suppression day and 11 of the individuals on the test day . day minus test day, non-aversive hours of sup- The probability of obtaining this result if co- pression day minus test day, and non-aversive efficients of both sign were equally probable hours minus aversive hours of the suppression is about 5 % for the test day, but the control-day day. The resulting differences were analysed in result is not significant (binomial test) . There two ways: (i) rank sign test for each group to was no difference in response duration between indicate divergence of the differences from zero ; control and test days (P > 0 . 1 by sign rank test (ii) parametric, two-way analysis of variance and analysis of variance of daily differences, with variable categories of ectoparasite and n = 13). deprivation treatment groups . The clean group showed more variability Running difference. A final statistic was between individuals (SD = 24 for daily estimates, calculated to indicate response to aversive n = 8) than within individuals (mean SD = 7 stimulation while allowing for the effects of for hourly estimates of eight fish) . Parasitized repeated exposure to the stimuli . A running individuals showed less variability (SD = 15 difference was calculated by subtracting the and 3, respectively, n = 5, probability of hourly estimates for each aversive hour from the equality to the clean group < 0 .05 by F test) . hourly estimates for the immediately preceding Low variability was caused by parasitized and following non-aversive hours . The average animals spending nearly all of the time in the of the six differences for each individual was response box. Differences in variability dictate tabulated as the running difference for that caution in interpreting the analysis of variance . individual and analysed in the same manner as However, the rank sum test and inspection of the daily differences above . Fig . 2 provide ample support of the differences between parasitized and clean individuals . Results Tilt (Fig. 3). Parasitized fish showed about Zebrasoma flavescens 30 yo less tilt behaviour than clean fish toward Response (Fig. 2). Parasitized individuals the end of the test day. This trend was supported spent nearly twice as much time in the response only by the analysis of variance of the hourly box as clean individuals (P < 0.01 by rank sum estimates (P < 0.01, n = 78). The more con- test and analysis of variance of daily estimates, servative analysis of daily estimates indicated no n = 13) . differences. This disparity probably resulted from the overlap between groups early in the test day rather than the inflated sample size of the analysis of hourly estimates . Fin-erect (Fig. 4). Parasitized fish performed 50- nearly twice as much fin-erect behaviour as

100 QW. 0 1 2 3 4 5 6 rlrilrlrJ]]HOUR Fig. 2 . Percentage of the time spent in the response box containing the cleaner model for Z. flavescens. Response duration is the average hourly estimate for each group 0 during each consecutive hour . Duration is expressed as a 1 2 3 4III5 6 percentage of the maximum possible response . The pair of HOUR _ histograms for each hour depicts the clean group in the open bar on the left (eight individuals) and the para- Fig. 3 . Percentage of the time spent in the tilt position sitized group in the closed bar on the right (five in- while in thenrsrri response box for Z. flavescens. See legend dividuals) . for Fig. 2.

LOSEY : CAUSES OF CLEANING 6 75

clean fish (P < 0 . 05 by rank sum test and ana- Twitch and jump (Figs. 6 and 7). Parasitized lysis of variance of daily estimates, n = 13). fish seemed to show more twitch and jump Parasitized fish maintained erect fins during behaviour toward the end of the test day . Due nearly all of the time that they spent in the to the large number of zero counts, only the response box . rank sum test for daily estimates could be Fin-erect was positively correlated to time applied (P < 0 . 05 and 0 . 05 < P 0-1, res- in-box for parasitized individuals (P < 0 .05 pectively, n = 13) . by correlation coefficient for hourly estimates, Incidental observations. Twitch, jump, and n -= 30). I regard this test as important regard- wag usually appeared in conflict situations such less of the inflated sample size because it was as when leaving and before entering the response performed to guard against confounding relation- box. These fast movements were particularly ships between dependent variables . It suggests striking in this species since isolated individuals that the correlation between parasites and fin- are usually slow-moving and best described as erect could have resulted from a causal relation- dull to observe. Chafe was rarely seen. ship between fin-erect and remaining in the response box for long periods . There may not Chaetodon auriga be a direct causal influence of parasites on fin- The conclusions of the early and final studies erect. were nearly identical. Since the final study Wag (Fig. 5). Parasitized fish appeared to employed a more effective design, Figs . 8 to 13 show more wag behaviour than clean fish are based on these data alone. The early study in the last 3 h of the test day, but this difference will be mentioned only when the results con- was tenuous . Hourly estimates were not analysed flicted with those of the final study . due to a large number of zero counts . Response (Fig. 8). Time spent in the response Daily estimates indicated a significant difference box was not related to parasite group (P > 0 . 1 by analysis of variance (P < 0.01, n = 13) but for all tests, n = 19 to 120) . not by rank sum test . Deprivation groups did not differ on the control day before deprivation (P > 0 . 1 by all tests, n = 19 to 120). Deprivation resulted in a

50 - 0 . 4

02 - 0 1 2 3 4 5 6 HOUR 0 Fig . 4. Percentage of the time spent with fin-erect while in 1 2 3 4 5 6 the response box111111 for Z. flavescens, See legend for Fig. 2. HOUR Fig. 6. Number of twitch actions per minute for Z . 0 . 4 - z flavescens . See legend for Fig. 5.

0-2- Wa 0-2- Z 0 W 3 011 - 0 3 4 5 6 HOUR 0 - Rr Fig . 5 . Number of wag actions per minute for Z.flavescens . 1 3 4 5 The number of actions is the average hourly estimate for 1 HOUR I each group with a single 9-min sample in each hour for each individual . Histogram pairs and sample sizes are Fig. 7 . Number of jump actions per minute for Z . as in Fig . 2 . flavescens. See legend for Fig. 5.

67 6 ANIMAL BEHAVIOUR, 27, 3

stronger response by the deprived group on the sign rank test of daily differences, n = 20) . test and suppression days (P < 0 .01 by analysis This increased response on the suppression day of variance of daily estimates, n = 20). Inter- was not seen in non-deprived animals in either action between parasite and deprivation factors study. on the control day (P < 0 .05 by analysis of Response duration showed some indications variance of hourly estimates only, n = 120) of increase during the control day (P < 0 .05 was not repeated on subsequent days . Deprived for early study ; 0.05 < P < 0 . 1 for final study by fish also showed a greater resistance to sup- analysis of covariance of hourly estimates, pression by the aversive stimulus (P < 0 .01 by n = 114 and 120, respectively) . However, this analysis of variance of daily differences and relationship was highly variable and the cor- running difference, n = 20). relation coefficients for the 12-min measures Illumination of the response box by a spot- on each individual varied randomly between light as an aversive stimulus reduced response positive and negative signs (binomial test) . duration while the box was illuminated (P < 0 .01 Response duration was reduced after initial by sign test rank of daily differences and running exposure to the model on the test day (P < 0 .01 difference, n = 20). Response by deprived fish by analysis of variance of hourly means, n = on the suppression day during hours when the 120), but the form of the reduction varied box was not illuminated (non-aversive hours) between individuals . Several fish showed a was higher than on the test day (P < 0 .05 by decreasing response over the first 4 to 5 h only sign rank test of daily differences, n = 20). This to increase their response in the final hour . The was not an after-effect of aversive stimulation, most consistent effect of any group was shown since response was also higher in the first hour by the deprived fish in the final study . Seven out of the suppression day prior to their first ex- of 10 had a negative correlation coefficient for posure to the aversive stimulus (P < 0.05 by 12-min measures, but this proportion does not indicate a significant trend (binomial test) . 100 - TEST DAY Examination of the 12-min measure for response bout length gives clearer results . Sixteen of the 20 individuals had a negative correlation co- 50 efficient for this measure on the test day . The probability of obtaining this result if there were random change in bout length is less than 5 w ~E o (binomial test) .

W I 2 3 4 5 6 7 F HOUR Fig . 8. Percentage of the time spent in the response box containing the cleaner model for C. auriga in the final study. Response duration is the average hourly estimate for each group during each consecutive hour . Duration is expressed as a percentage of the maximum possible response . Sample size is five for each of the four groups. The four histograms describing the groups for each hour are, from left to right : non-deprived, unparasitized fish (open bar) ; non-deprived, parasitized fish (closed bar) ; I 2 3 4 5 6 7 deprived, unparasitized fish (light stippled bar) ; and HOUR deprived, parasitized fish (dark stippled bar) . The star symbols depict the bare-wire control group for the test day only (eight individuals) . The bar on the abscissa Fig. 9 . Percentage of the time spent in the tilt position for the suppression day indicates the 3 h when the while in the response box for C. auriga in the final study . aversive `spotlight' was illuminated . See legend for Fig. 8.

LOSEY : CAUSES OF CLEANING 677

Tilt (Fig. 9). Tilt was not related to parasite day before the first exposure to the aversive group (P > 0.1 for all tests, n = 19 to 120). stimulus (P > 0 . 1 by analysis of variance of daily Tilt was slightly higher in deprived animals differences, n = 20). However, the effects of (P < 0 .05 by analysis of variance of daily aversive stimuli were slight. All analyses for estimates, n = 20). Tilt was strongly correlated relationship between aversive stimuli and fin- to the amount of time spent in the response box erect behaviour were non-significant. I conclude during the videotaped observations for both that aversive stimuli produced a slight increase deprivation groups (P < 0.01 by correlation in fin-erect behaviour, but only in deprived coefficient for hourly estimates, n = 60). This animals. suggests that tilt occurred whenever a long bout Wag (Fig. 11). Wag was indicated as being of in-box appeared, and that it was not directly reduced in parasitized animals on the test day influenced by deprivation . Bout-by-bout data (P < 0.01 by analysis of variance of hourly are not available, but my subjective impressions estimates, n = 120). This effect was not sup- support this possibility and I discount any direct ported by other analyses without inflated sample causal relationship between tilt and deprivation . size, and I attach little significance to the trend . Tilt showed some correlation to aversive Wag showed less difference between aversive stimuli. However, these can all be explained by and non-aversive hours on the suppression day the correlation between tilt and time in-box . in deprived animals than in non-deprived Fin-erect (Fig. 10). Parasitized fish tended to animals (P < 0 .05 by analysis of variance of show less fin-erect behaviour than clean fish daily differences, 0 .05 < P < 0 . 1 by analysis in the final study only (P < 0 .05 by analysis of of variance of running difference, n = 20) . variance of daily estimates, n = 20). The magni- There was a weak indication that deprived tude of the effect was small and showed much animals showed less wag than non-deprived variability between individuals. fish on the test day (0 .05 < P < 0 . 1 by analysis Deprived fish showed more fin-erect behaviour of variance of hourly estimates, n = 120), but than non-deprived animals on the suppression this was not supported by analyses without an day, but this was seen only in the daily difference inflated sample size. statistic (P < 0.05 by analysis of variance, n = Aversive stimuli were associated with some 20). Deprived fish differed from non-deprived increase in wag as compared to the test day fish in the amount of fin-erect time on the (P < 0.05 by sign rank test of daily differences, suppression day only as compared to the amount shown on the test day . The effects of deprivation were not present on hour I of the suppression

I IL.11, . IL I

11-00119∎$;R .11111 of%

Fig. 11 . Number of wag actions per minute for C. auriga in the final study . The number of actions is the average Fig. 10. Percentage of the time spent with fin-erect while hourly estimate for each group with a single 9-min in the response box for C. auriga in the final study. See sample in each hour for each individual . Histograms and legend for Fig. 8. sample sizes are as in Fig. 8. 678 ANIMAL BEHAVIOUR, 27, 3 n = 20). This effect was not seen in hour 1 of Incidental observations . Most of the fish the suppression day . that failed to meet the response criterion did Twitch (Fig. 12). There was a weak indication show attraction to the model . Some apparently that more heavily parasitized animals twitched failed to discover how to enter the transparent less than others in the early study (P < 0 .05 response box . Others appeared to be frightened by analysis of variance of daily means, n = 19 ; of the box. Fish that did learn the response 0.05 < P < 0 . 1 by analysis of variance of developed persistent adventitious behaviour in daily differences, n = 19) . This trend was not their manner of approaching, entering, turning seen in the final study. inside the box, and exiting. The conceptually Deprived animals tended to show less twitch simple task of responding to the model in the than non-deprived fish, but only during the non- box appeared to comprise a complex series of aversive hours of the suppression day (P < 0 .01 conditioned behavioural patterns . by analysis of variance of running difference, Wag, twitch, and jump behaviour were com- n = 20; 0.05 < P < 0.01 by analysis of variance mon in situations that evidenced approach- of daily differences, n = 20). withdrawal conflict . This included approaching Aversive stimuli increased twitching, but the response box but failing to enter, and just there was a more significant increase during non- prior to and after leaving the box . These action aversive hours (P < 0 .01) than during aversive patterns frequently accompanied fast swimming hours (P < 0 .05 by analysis of variance of daily around the tank . differences, n = 20). This effect was not present Chafe behaviour was rare. It was about twice in hour 1 of the suppression day . as common in deprived fish as in non-deprived fish, and about three times as common on the Jump (Fig. 13). Parasitized fish showed less suppression day as on the test day for all fish . jumping than clean fish during the non-aversive hours of the suppression day (P < 0 .01 by Control animals . Due to time restrictions no- analysis of variance of daily differences, n = 20), wire controls were discontinued after running but not during other periods of the experiment . only two fish. Both fish gave virtually no Deprivation showed no effects. response and rarely performed any of the action Aversive stimuli increased the amount of patterns. My experience with these fish suggests jumping (P < 0.05 by analysis of variance of that this would be representative of C . auriga. daily differences, n = 20). This was evidenced The data for all eight bare-wire control fish only during the non-aversive hours of the were considered together . Their behaviour was suppression day after the first exposure to the similar to that of the test fish. Response duration aversive stimulus. tended to be higher than that of the parasitized

z

d SUPPRESSION DAY

Fig. 12 . Number of twitch actions per minute for C. Fig. 13 . Number of jump actions per minute for C . auriga in the final study. See legend for Fig . 11 . auriga in the final study. See legend for Fig . 11.

LOSEY : CAUSES OF CLEANING 679

test fish (Fig . 8, P < 0 .05 by analysis of variance variability between individuals cast doubt on of hourly estimates, n = 118) . This difference the validity of the conclusion that ectoparasites was not supported by analysis of daily estimates have no effect. Statistically significant cor- without inflated sample size . This disparity may relations might be shown with considerable have resulted from the overlap between the increase in sample size and further efforts to groups late in the day as well as from the in- isolate uncontrolled sources of variability . flated sample size of the analysis of hourly Such efforts might clarify many details of estimates. the causes of host behaviour, but I doubt that they would be of much value for Discussion understanding the general form of the host's My results indicate three behavioural factors responses. The present experimental technique that could have easily observable effects on has proven to be capable of revealing major cleaning symbiotic interactions : presence of causal effects as well as a variety of subtle and ectoparasites increases response duration in Z . highly variable behavioural phenomena. How- flavescens, and deprivation increases response ever, some variables, particularly ectoparasitic duration, while aversive stimulation decreases infections for C. auriga, have shown little effect . response duration in C. auriga. The remainder This result prompts a re-evaluation of cleaning of the behavioural findings give insight as to the symbiotic behaviour . causes of host responses, but probably have little effect in shaping the general form of the Effects of Experimental Treatments response of hosts to cleaners . Figures 14 and 15 provide a summary of all Much of my discussion centres on the lack of statistical results that were not discounted correlation between ectoparasites and host above . In-box bout length is a dependent variable behaviour . However, low sample sizes and high but, since it seemed to affect some of the other behavioural patterns, it is discussed as an

INDEPENDENT DEPENDENT independent variable. VARIABLE VARIABLE Several hours of exposure to the model produced a slight decrease in response duration Response in both species.

Exposure INDEPENDENT DEPENDENT Jump

Twitch

Wag Ectoporasites

Fin erect

Tilt In box bout length

Fig . 14 . Statistical relationships between independent variables or treatments and dependent variables in Z . flavescens. Arrows indicate that the treatment was associ- ated with higher (open arrows) or lower (solid arrows) levels of the respective behaviour . The width of the arrows indicates the approximate magnitude of the effect and statistical confidence. The narrowest arrows indicate relationships that are of questionable validity and Fig. 15 . Statistical relationships between independent importance. These arrows are only indications of possible variables or treatments and dependent variables in C. causal relationships . auriga . See legend for Fig . 14.

680 ANIMAL BEHAVIOUR, 27, 3

Parasitized Z. flavescens showed much more Structure of the Causal Systems response than unparasitized fish, but this was The foregoing discussion provides clues not true for C. auriga. Jump, wag, and twitch, about the structure of the causal systems for actions that appear to serve as warning signals host behaviour in C. auriga and, possibly, Z . to cleaners (e .g. Feder 1966), were somewhat flavescens. The actual structure is undoubtedly higher in parasitized Z. flavescens and lower in more complex than the hypothesis presented here parasitized C. auriga. In Z. flavescens, most of and may differ in unrelated species. the differences were only seen in the last 2 or 3 h . Tactile reward. Response duration in this In C. auriga, the results for wag and twitch were study indicated the strength of the tendency not convincing . However, similar findings for to respond to a cleaner (Losey 1977) . This all three actions suggests that the effect may be tendency seems to be based on a tactile sensory/ real but of small magnitude and difficult to perceptual system . This system facilitates beha- detect with small sample sizes. Fin-erect, an viour that results in gentle tactile stimulation element of posing or solicitation behaviour, such as approaching a model or a cleaner . showed the same relationship to ectoparasites Response to tactile reward results in flexible as the warning signals for both species . Tilt, visual responses . Hosts respond to unrealistic the second element of posing behaviour, showed models, including fishing lures, almost as well the opposite effect, but only late in the day . as to realistic models (Losey 1972b) . The behaviour of both species appeared to Response to tactile reward decreases after be altered when they spent long periods of time prolonged exposure to tactile stimulation . in the response box. Z. flavescens showed more However, evidence of negative feedback was fin-erect and C. auriga evidenced more tilt. variable and slight . After 6 h of exposure to the Illuminating a spotlight over the response model, the fish could hardly be called satiated . box inhibited response in C. auriga and was Such findings might indicate experimental or associated with some increase in jump, wag, conceptual error . McFarland & Sibly (1972) twitch, and fin-erect . However, this increase suggested that some motivational systems may was usually evident only after cessation of the escape accurate assessment . The stimulus state or aversive stimulus. combination that would consummate the system (bring all of its driving variables to a zero state) Depriving the fish of exposure to the cleaner is outside of the possible universe of such states model for two days produced an increase in provided by the experiment . There might be con- response in C. auriga . Effects of deprivation summatory stimuli from a living cleaner that on twitch, wag, and fin-erect were seen only serve to satiate response to tactile reward, but after the fish had experienced the aversive are not provided by the model . Decrement of stimulus and then only after the aversive stimulus response in this experiment might have resulted had been removed. Fin-erect showed some from habituation to the model that lacked these increase in deprived animals, while twitch and critical stimuli . wag evidenced a slight decrease . Jump showed Several lines of evidence suggest that this is no relationship, but this was not surprising not so. The model is a strong reinforcer . since the jump data was plagued by a large C. auriga have responded to a model on a number of zero counts . discrete trial schedule for many days without The strong response of fish to a bare wire decrement in performance (Losey & Margules suggests that tactile stimuli are the basis for the 1974, unpublished data) . Bouts of interaction reinforcing properties of the cleaner model . with a cleaner frequently terminate when the host leaves after receiving bites from the cleaner Losey (1971, 1974) and Losey & Margules (Losey 1971) or other aversive stimuli (Losey (1974) suggested the importance of tactile 1977) and not by satiation. Aversive stimuli stimulation by cleaners. Cleaners provide both from the cleaner produce a brief decrement in gentle tactile stimuli and aversive stimulation response to both cleaner and model, and are such as biting the host and violating its personal accompanied by avoidance and conflict beha- space when it is not soliciting the services of the viour (Losey 1977) . This supports the view that cleaner. Losey (1977) held that cleaner models suppression of response terminates interactions, were more effective than living cleaners at not consummatory stimuli such as `relieving eliciting symbiotic responses since they lacked an itch'. However, it would be difficult to demon- the aversive stimuli. strate that ectoparasite removal has no effect . LOSEY : CAUSES OF CLEANING 681

Conflict behaviour . Jump, twitch, wag, and and exposes ectoparasites to predation . Cleaners fin-erect were indicated as expressions of moti- are warned of possible danger by perceiving vational conflict between the tendencies to jump, wag, and twitch as expressions of conflict, approach and withdraw from the response box . and leave the host. These conclusions suggest Chafe can probably be included in this list, the popular interpretation that cleaning is a but it was observed too rarely to allow analysis . mutualistic or even altruistic relationship with Aversive stimulation reduced response duration special symbiotic signals and responses (e.g. in C. auriga and can be pictured as increasing Trivers 1971 ; but see Gorlick et al . 1978). its tendency to withdraw from the response box. Knowledge of the causal basis for this beha- Aversive stimulation was associated with slight viour now leads to somewhat different con- and variable increases in jump, wag, twitch, clusions for these species . Responses to tactile and fin-erect. In addition, the effects of depriva- reward result in attraction of fish to cleaners, tion on these patterns were seen only after the but the causal system for these responses is fish had experienced the aversive stimulus poorly adapted to the ultimate functions of the coupled with the formerly attractive stimulus of symbiosis . Input from ectoparasites is absent or the cleaner model . Jump, twitch, and wag also incomplete as a motivational factor . The only occur as components of the social behaviour of indication of consummation of response is C. auriga in situations where agonistic conflict without obvious function in the field : its time would be expected (personal observation) . requirements (hours) are greater than the I had predicted an increase in conflict beha- duration of interactions with cleaners (seconds) . viour in deprived animals : their greater response Immediate results and causation are closer to should cause frequent conflict by bringing them tactile hedonism than to control of ectoparasites . close to the aversive stimulus . But only fin-erect Thresher (1977) has observed `hedonistic' fish was greater in deprived fish. These actions might posing for gorgonians (soft corals) in the field not all be expressions of approach-withdrawal that wave against their sides and deliver tactile conflict, or they might have somewhat different stimulation. causal relationships in addition to simple Jump, wag, twitch, and fin-erect are imper- conflict. Variability in the occurrence of conflict fectly adapted as symbiotic signals . In Z. behaviour would be expected, since it is probably flavescens, they appear to be reliable expressions influenced by many factors that were not con- of conflict. In C. auriga, deprivation may produce trolled in this study. Such behavioural patterns changes that are of advantage to the host ; may also be important during social interactions . fin-erect, an element of solicitation behaviour, Differences in the apparent effects on these is increased while the purported warning signals behavioural patterns could also result as an (twitch and wag) decrease . However, ecto- artifact of my observation methods . Fin-erect parasites inhibit all four behaviour patterns was tabulated as the percentage of time in the regardless of their functions . response box close to the aversive stimulus . Jump, wag, and twitch were tabulated when in Evolution any location. Assuming that the tendency to Existing hypotheses on the evolution of withdraw was strongest when close to the cleaning symbiosis depict a co-operative evolu- aversive stimulus (e .g. Miller 1959), differences tionary history . Aside from Trivers's (1971) in the context of the behavioural patterns may hypothesis for altruistic evolution, authors have have been critical . Deprivation treatment altered avoided precise formulation of a general the amount of time spent next to the aversive hypothesis . Wyman & Ward (1972) proposed a stimulus. I can erect a hypothesis that would hypothesis for the evolution of cleaning between explain the disparate results based on the method two cichlid species, but it cannot be applied to of tabulation as a confounding effect . However, reef fishes . Most authors have implied that host I lack the data to test any such hypothesis, and species probably encountered cleaner precursors I doubt the value of such a priori exercises . that occasionally fed on ectoparasites . Under the influence of selective pressure for the removal Functional Significance of ectoparasites, hosts evolved special symbiotic All authors have agreed on the functional responses and signals to maximize the adaptive results of the host's behavioural patterns (Eibl- value of the symbiosis. Eibesfeldt 1955 ; Feder 1966 ; Wickler 1968 ; It is difficult to explain many recent behaviour- Losey 1971 ; Potts 1973) . Posing attracts cleaners al and ecological findings with this hypothesis . 682 ANIMAL BEHAVIOUR, 27, 3

Hobson (1971) criticized Feder's (1966) con- for tactile reward did not originate to control clusions on differences between tropical and or maximize the efficiency of the symbiosis . temperate cleaners, but many differences re- Gentle tactile stimuli appear rewarding to most main. Both tropical and temperate cleaners if not all vertebrates (e.g. Pepper & Beach 1972) have specialized behaviour but the specializa- and may serve various other functions (see tions differ (Hobson 1971 ; Potts 1973). The below). most brightly coloured cleaners, Labroides spp ., Prior existence of conflict behaviour is sup- are found in the tropics . California host fish ported by the use of the same actions in social must show solicitation behaviour, and they behaviour and their imperfect alignment to the compete for cleaners (Hobson 1971). Tropical functions of cleaning. The inhibition that ecto- cleaners such as Labroides spp . pursue many of parasites exert over all forms of conflict beha- their hosts, and much cleaning is performed viour, regardless of their function, may persist without solicitation by their hosts (Losey 1971, as another evolutionary artifact in C. auriga . 1972a, 1974). The adaptive significance of clean- Such inhibition could be a first approximation ing in some tropical areas is doubtful to providing a motivational input from ecto- (Youngbluth 1968 ; Losey 1972a, 1974), but parasites, ectoparasite removal may be more important Many modern fishes exist as ectoparasites in other areas such as California and Puerto Rico (Marlier & Lelup 1954; Hoese 1966 ; Hobson (Hobson 1971 ; Losey 1974) . My present results 1968 ; Roberts 1970; Major 1973) . Most of these suggest that some tropical host fishes are not parasites provide strongly aversive stimuli to highly specialized for cleaning, but many their hosts, but others merely graze on mucus tropical cleaners are highly specialized . without painful biting (Hobson 1968) . Some of I suggest an alternate hypothesis for the these fish parasitize behavioural responses of evolution of cleaning . This symbiosis has un- their hosts through aggressive mimicry (Wickler doubtedly had several separate origins and 1963, 1968 ; Springer & Smith-Vaniz 1972 ; evolutionary histories . This hypothesis need not Losey 1972c, 1975) . Cleaners retain most, if not apply to all areas or to all species . It is aimed at all, of the aversive stimuli of their probable tropical Indo-Pacific cleaning symbiosis, and at predecessors and appear to have parasitized Labroides spp . of cleaners. I will first present the the causal system for response to tactile stimu- hypothesis and then support for each of its lation in their hosts . elements. The provision of positive reinforcement by My results suggest that the basic structure of these early cleaners would open an unexploited the causal systems for host behaviour did not feeding niche . Host solicitation and immobility originate to fulfil symbiotic functions . I propose would enable cleaners to find ectoparasites, which that the causal systems that govern responses to I imagine form a rich food supply . The per- tactile reward and expressions of conflict sistence of parasitic modes of feeding (mucus, existed prior to the origin of cleaning . The scales, and tissues) in most cleaners suggests precursors of modern cleaners were probably that ectoparasites might not be a reliable or unspecialized fish that occasionally fed on ecto- constant food source . The strong advantages parasites, mucus, scales, and skin from their of this niche would favour evolution of effective hosts. These cleaner precursors exploited the tactile stimuli and unique colorations and tendency in their hosts to respond to tactile behaviour that could facilitate recognition of reward. Such exploitation allowed them to gain cleaners. The danger of attack would force ready access to their food supply and the ability the formation of responses to expressions of to find and feed on ectoparasites . Since that time conflict by their hosts and other signs of danger. cleaners have evolved into highly specialized Potts (1973) found that the cleaner Labroides symbionts. Host species have shown little diridiatus appeared to learn different methods evolutionary change due to variable and fre- of inspection and areas of danger for each host quently weak selective forces . species. Prior existence of response to tactile reward Survival value for hosts appears to be variable is suggested by the lack of agreement between and probably weak in some places or at some this system and the ultimate function of cleaning. times. Hosts are subject to several costs, but The lack of ectoparasitic control and functional their importance has not been studied . Hosts consummatory feedback may persist as artifacts lose mucus, scales, and tissues along with ecto- of the evolutionary pathway : the causal system parasites. These costs are probably minimal

LOSEY : CAUSES OF CLEANING 6 8 3

since little is removed from each host . Other be farther along the evolutionary path toward investments such as time spent with a cleaner, maximizing the benefits of cleaning symbiosis . energy expenditure while travelling to a cleaner, My hypothesis raises several questions that and exposure to predation while posing all can only be given speculative answers at this appear to be slight . time. If tactile reward is sufficient to allow the All authors have agreed that ectoparasite development of a symbiosis, why is it not removal can be of survival advantage to hosts . indicated in other behavioural contexts? Tactile However, there is disagreement as to the im- reward probably does contribute to other types portance of these advantages . All reports that of behaviour. Some hosts might respond differ- cleaning is vital to fishes are based on subjective ently to cleaners because this causal system has impressions (Limbaugh 1961) or aquarium been modified as a result of other functions. The observations (Wyman & Ward 1972) . Some behaviour of some cichlid parents during glan- studies have indicated that cleaners are not cing by their young (Ward & Barlow 1967 ; necessary for control of ectoparasites and might Noakes & Barlow 1973) might be shaped by exist as parasites themselves (Youngbluth 1968 ; this sytem . Wyman & Ward (1972) suggested Losey 1972a) . Studies in other areas have given that this behaviour was important in the evolu- indirect (Losey 1974) and direct (Hobson 1971) tion of cleaning in some cichlids . Tactile stimuli evidence that cleaners could be effective in might favour schooling in species with closely ectoparasite control. The most thorough study packed groups such as young scarid fishes has shown that, while cleaning was a statistically (personal observation) . There may be many significant factor in regulating ectoparasite other examples where tactile stimuli are impor- populations for the species studied, effects were tant but have been ignored due to our pre- subtle (Atkins & Gorlick MS .). Cleaners were dilection for attending to visual and acoustic not vital . Other control mechanisms were nearly stimuli . as effective in the absence of cleaning. What prevents fish from merely rubbing against any available surface? Many fish do I conclude that cleaning may exist as a mutual- ism when there is a high recruitment rate for rub against objects or respond to tactile stimula- ectoparasites, and/or other control mechanisms tion by animals such as gorgonians (Thresner are inadequate. But it may also exist as a com- 1977). However, this behaviour is far less com- mensalism or even parasitism when ecto- mon than would be expected based on my parasites are of little importance (Losey 1972a) . results. I suggest a three-part explanation . First, Mutualism appears to be most likely in temperate response to self-induced stimulation may be . reduced as it is in humans . Second, response to areas such as California tactile stimuli from cleaners may have been My evolutionary hypothesis can explain the amplified by selective pressure for ectoparasite similar behaviour shown by various species of removal ; but I suspect that the reverse is true . hosts under different conditions of survival Anecdotal evidence has suggested that fish that value. Cleaners have exploited tactile reward as a live in areas where cleaners and other sources of behavioural `building block' in different host tactile stimuli occur may be less susceptible to species. The same building blocks are indicated the effects of tactile stimuli than others . After in C. auriga and Z. flavescens, but they have placing them in an aquarium with a cleaner, I evolved along different lines toward the realiza- have observed small blennies (Istiblennius sp.) tion of maximum benefits from cleaning sym- that live in high tidal pools avoid the cleaner's biosis. Continued investigation of other species advances. However, after a few days they spent should reveal a variety of analogous evolutionary nearly all of their time following the cleaner and paths. soliciting its services . Their responses were far One might argue that if a behavioural response greater than any that I have observed in reef exists, it must be or have been adaptive or it fishes. After the death of the cleaner, they solicited would not be maintained in the population . cleaning from all of the other animals in the tank . However, behavioural relationships like those I Such observations can be misleading, but they have suggested can be resistant to change even lead me to speculate that this species differs thought they are imperfect adaptations . Cleaning from tropical reef fishes. Cleaners are never may be only one of many selective forces that found in high tidal pools, and these blennies are acting on response to tactile stimulation . would rarely encounter any form of mild tactile Host species that I have not studied may well stimulation in their barren, wave-swept habitat . 684 ANIMAL BEHAVIOUR, 27, 3

This species may lack inhibition for maladaptive REFERENCES response to tactile stimuli . A third answer may Atkins, P . & Gorlick, D. L. MS. Effects of cleaning behavior by Labroides dimidiatus on reef fish be that there are few sources of gentle tactile and ectoparasite populations. stimulation on a coral reef. Long, flexible Cheng, T. C . 1967 . Marine Molluscs as Hosts for Sym- gorgonians are rare on Indo-Pacific reefs where I bioses. Advances in Marine Biology, Vol . 5. have worked but are common in the Caribbean New York : Academic Press . where Thresher (1977) observed fish using them Eibl-Eibesfeldt, I. 1955 . Ober Symbiosen, Parasitismus, as sources of tactile stimulation . Species that and andere besondere zwischenartliche Beziehungen tropischer Meeresfische . Z. Tierpsychol., 12, live in areas where such stimuli are common 203-219. might give different results. Feder, H . M . 1966. Cleaning symbiosis in the marine How does host behaviour develop with some environment. In : Symbiosis, Vol. 1 (Ed . by S . M. Henry), pp. 327-380 . New York : Academic temperate cleaners that do not pursue their hosts Press . and deliver tactile stimuli? I suspect that Fricke, H. 1966 . Zum Verhalten des Putzerfisches, cleaning symbiosis may show profound differ- Labroides dimidiatus. Z. Tierpsychol., 23, 1-3 . ences between tropical, temperate, and fresh- Gorlick, D . L . 1978 . Cleaning symbiosis : factors control- water areas . Even within the tropics some host ling host species preference change in Labroides phthirophagus Randall . Ph.D. Dissertation, species are more specialized than others . University of Hawaii . Temperate host species may be even more Gorlick, D . L., Atkins, P. D . & Losey, G . S. 1978. specialized . Cleaning is usually initiated by the Cleaning stations as water holes, garbage dumps, host and not the cleaner (Hobson 1971) . If my and sites for the evolution of reciprocal altruism. conclusions on adaptive significance are correct, Am. Nat., 112, 341-353 . California host fish should be under stronger Hobson, E . S. 1968 . Predatory behavior of some shore fishes in the Gulf of California. U.S. Bureau Sport selective pressure than tropical Pacific hosts to Fisheries and Wildlife Research Report, 73, 1-92. develop cleaning symbiotic responses and com- Hobson, E. S. 1971 . Cleaning symbiosis among Cali- pete for the services of the cleaner . Study of fornia inshore fishes. Fishery Bull., 69, 491-523 . proximate causal factors in these species might Hoese, H . D. 1966 . Ectoparasitism by juvenile sea cat- reveal far more specialization than shown in fish, Galeichthys felis . Copeia, 1966, 880-881 . Limbaugh, C. 1961 . Cleaning symbiosis . Scient . Am., my study. 205,42-49. The evolutionary history of cleaning sym- Lincicome, D . R . 1971 . The goodness of parasitism . biosis may differ between areas as a function of In: Aspects of the Biology of Symbiosis (Ed. by T. C. Cheng), pp . 139-228 . Baltimore, Md .: the adaptive value of ectoparasite removal . University Park Press . Areas in which ectoparasites are of little impor- Losey, G . S . 1971 . Communication between fishes in tance may have specialized and even parasitic cleaning symbiosis. In : Aspects of the Biology of cleaners while the hosts remain unspecialized Symbiosis (Ed. by T . C . Cheng), pp . 45-76 . Baltimore, Md . : University Park Press. or have evolved away from cleaning responses . Losey, G . S . 1972a. The ecological importance of clean- Areas in which ectoparasites are critical may ing symbiosis . Copeia, 1972, 820-833 . have highly specialized hosts and perhaps less Losey, G . S. 1972b . Behavioral ecology of the "cleaning specialized cleaners . Future study of host fish". Aust. Nat. Hist., Sept. 1972,232-238 . Losey, G . S . 1972c . Predation protection in the poison- behaviour in other areas and critical study of fang blenny, Meiacanthus atrodorsalis, and its the adaptive significance of ectoparasites would mimics, Ecsenius bicolor and Runula laudandus provide a test of this hypothesis and improve (Blenniidae) . Pacific Sci., 26, 129-139 . Losey, G. S. 1974 . Cleaning symbiosis in Puerto Rico our understanding of the many forms of this with comparison to the tropical Pacific . Copeia, widespread symbiotic relationship . 1974, 960-970 . Losey, G. S. 1975. Meiacanthus atrodorsalis : Field evidence of predation protection . Copeia, 1975, Acknowledgments 574-576 . I thank my research assistants, Dennis Gorlick Losey, G . S. 1977 . The validity of animal models : A test for cleaning symbiosis . Biol. Behav., 2, and Paul Atkins, for their long hours of work . 223-238 . I also thank them and George Barlow for Losey, G. S . 1978 . The symbiotic behavior of fishes. In : reading an earlier version of the manuscript . The Behavior of Fish and Other Aquatic Animals This research was supported by NSF grant (Ed. by B . Mostofsky), pp . 1-31 . New York: Academic Press . no. BMS 74-03508-AOI . This paper is contri- Losey, G. S. & Margules, L. 1974 . Cleaning symbiosis bution no. 554 of the Hawaii Institute of Marine provides a positive reinforcer for fish . Science, Biology. N. Y., 184, 179-180 . LOSEY : CAUSES OF CLEANING 685

Major, P. F. 1973 . Scale feeding of the leatherjacket, Springer, V. G. & Smith-Vaniz, W . F . 1972. Mimetic Scomberoides laysan and two species of the genus relationships involving fishes of the family Blenni- Oligoplites (Pisces: Carangidae) . Copeia, 1973, idae . Smithsonian Contr . to Zool., 112, 1-36 . 151-154. Thresher, R. 1977 . Pseudo-cleaning behavior of Florida Marlier, G . & Lelup, N. 1954. A curious ecological reef fishes. Copeia, 1977, 768-769. `niche' among fishes of Lake Tanganyika . Nature, Trivers, R . L . 1971 . The evolution of reciprocal altruism . Lond., 174, 935-936. Q. Rev. Biol., 46, 35-57 . McFarland, D . & Sibly, R. 1972. Unitary drives re- Ward, J. A . & Barlow, G . W. 1967 . The maturation and visited. Anim. Behav., 20, 548-563 . regulation of glancing off the parents by young Miller, N . E. 1959 . Liberalization of basic S-R concepts . orange chromides (Etroplus maculatus-Pisces- In: Psychology : A Study of Science, Study I, Cichlidae) . Behaviour, 29, 1-56 . Vol. 2 (Ed. by S . Koch), pp. 196-292 . New York : Wickler, W. 1963 . Zum Problem der Signalbildung, am McGraw-Hill . Beispiel der Verhaltensmimikry zwischen Aspi- Noakes, D . L. G. & Barlow, G. W. 1973 . Ontogeny of dontus and Labroides (Pisces : Acanthopterygii) . Z. parent-contacting in young Cichlasoma citrinellum Tierpsychol., 20, 657-679 . (Pisces: Cichlidae) . Behaviour, 46, 221-255. Odum, E. P. 1959. Fundamentals of Ecology. Philadelphia, Wickler, W . 1968 . Mimicry in Plants and Animals . Pa. : W. B . Saunders Co . New York : McGraw-Hill . Pepper, R . L. & Beach, F. A., III . 1972 . Preliminary Wyman, R. L . & Ward, J. A. 1972 . A cleaning symbiosis investigations of tactile reinforcement in the between the cichlid fishes Etroplus maculatus and dolphin. Cetology, 7, 1-8 . Etroplus suratensis. I. Description and possible Potts, G . W. 1973 . The ethology of Labroides dimidiatus evolution. Copeia, 1972, 834-838 . Cuv. and Val.) (Labridae : Pisces) on Aldabra . Youngbluth, M . J. 1968 . Aspects of the ecology and Anim. Behav., 21, 250-291 . ethology of the cleaning fish, Labroides phthiro- Roberts, T. R. 1970. Scale-eating American characoid phagus Randall . Z. Tierpsychol., 25, 915-932 . fishes with special references to Probolodus heterostomus. Proc. Calif. Acad. Sci. (Fourth (Received 11 January 1977 ; revised 1 September 1978 ; Series), 38, 383-390. MS. number : A1978)